Inertial navigation has been in use for a considerable amount of time. In operation, given an initial position of a device, its position can be tracked using various sensors that detect a change in inertia in the device. However, to provide accurate tracking the sensors being used must be very sensitive and accurate. This is impractical for tracking a device such as a smart phone or other mobile communication device. In particular, inertial navigation using the relatively inaccurate motion sensors found in smart phones is a difficult problem due to drift, accumulated calculation error, and the inability to provide the system with a known instant where all motion has stopped, i.e. the sensors and associated processing in a smart phone may be unable to determine whether the device is moving at a slow, constant rate or it is stopped.
Doppler assisted inertial navigation (DAIN) was introduced to augment inertial navigation system by measuring a frequency shift from an echo of a signal being broadcast by the device. These systems combine Doppler velocity measurements that inherently don't drift in order to correct inertial systems that have significant drift. Many such systems were based upon radar signals from the ground to targets in the air. Similar echo-based techniques were applied using acoustics for the autonomous navigation of underwater vehicles. In this configuration, sonar provided the Doppler information. More specific to the scope of the present invention, systems were proposed that place an echo-based Doppler transceiver in a mobile computer to provide the DAIN function. However, adding such a system to a smart phone would add a significant cost and complexity.
Accordingly, there is a need for a technique to correct inertial navigation in a mobile device. It would also be beneficial if this could be accomplished in a smart phone without modification of its existing hardware.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.